Airborne weather radar systems which provide CRT screen displays showing weather information such as precipitation and/or turbulence in accordance with range and azimuth positions have come into wide spread use. The displays provided by these units follow the conventional planned position indicator (PPI) format of having range displayed radially outward from a central point at the bottom of the display and azimuth displayed across the screen along circular lines radially equal distance from the same central point. This type of display correlates with a sweep of a radar antenna through a range of azimuth positions as it scans the radar beam from side to side. The weather information provided by such weather radar system is extremely useful but it has been shown to be less than optimal, especially when range and height information are also desired, as suggested in the above referenced patent application. In order to accommodate both PPI and RHI weather radar information on the same display, it will be necessary to be able to move a standard PPI display to a different position on a display screen and simultaneously reduce the overall size of the PPI display.
Also, weather radar engineers are continuously developing new methods for detecting storm cells at greater distances and with greater accuracy. One of these new methods for improving storm detection involves substantially increasing the overall time for a weather radar antenna to make one complete scanning cycle. While this change does provide several advantages, it also has several drawbacks. One major drawback with a prolonged scan cycle is that the update rate for the new weather radar information is greatly reduced. Consequently, the forward motion of an aircraft and any turning maneuvers cause the standard PPI display to not accurately reflect the present situation outside of the aircraft. A translation or rotation of the data is needed to provide an appropriate representation of the relative position of any storm cells.
In the past, translations and rotations of the weather radar data have been accomplished by various means. However, there has frequently been a degradation of the display associated with each rotation or translation. Moreover, if several rotations or translations were necessary before a data update, the degradations associated with one rotation or translation would be incorporated into the next rotation or translation thereby compounding the degradation problems.
Consequently, there exists a need for improving the ability to move a standard PPI display to different positions on a display screen while comcomitantly allowing for a reduction or expansion of the overall size of the PPI display; and for translating and rotating weather radar data through a series of rotations and translations without compounding the display degradation.